1. Field of the Invention
The present invention relates to an offset detecting system of an acceleration sensor, an offset detecting method of an acceleration sensor, and an offset detecting program of an acceleration sensor, and a navigation system, and is applicable to a navigation system to be installed in a vehicle, for example.
2. Description of the Related Art
Heretofore, a navigation system to be installed in a moving mobile body or the like in that the present position is calculated based on a GPS signal transmitted from a Global Positioning System (GPS) satellite, and the position and the forward direction of the above mobile body are displayed on a map screen has been widely popularized.
In such navigation system, the velocity and the forward direction of the mobile body are calculated using an acceleration sensor for detecting the acceleration of the mobile body in the forward direction and a gyro sensor (yaw rate sensor) for detecting the rotary angular velocity of the above mobile body in a horizontal direction. Thereby, the present position of the mobile body can be estimated even in the case where a GPS signal cannot be received in the shade of a building and in a tunnel, for example.
However, this acceleration sensor had a problem that output voltage when acceleration was not detected, so-called zero gravity offset varies, by the effect of the surrounding temperature, generation of heat by the navigation system itself, or the like, by its temperature characteristic.
Then, some navigation systems in which an amount of height change (height difference) is calculated using that the forward direction component of gravity acceleration is included in a detected value by an acceleration sensor when the vehicle runs on a slope, and a zero gravity offset (acceleration error) is calculated by comparing the calculated amount of height change to the known amount of height change based on height data stored in map information or the like have been proposed (see Japanese Patent Laid-Open No. 2004-233306, for example).